Not Applicable.
The present invention relates generally to the design of wheels and wheel components used with omni-directional vehicles employed in commercial, medical, industrial, and recreational settings.
Omni-directional vehicles capable of controlled motion in any direction have long been recognized as having many useful applications. A number of designs of omni-directional vehicles have been disclosed. Most omni-directional vehicle designs are simliar in that they use wheels that feature a number of rollers positioned about the periphery of the wheel; the rollers permit the wheels to support motion in directions at an angle to the wheel""s plane of rotation. Omni-directional vehicles using such omni-directional wheels can move in any direction by rotating the wheels and rollers in an appropriate combination. Each omni-directional wheel""s rotation is mechanically driven and servo controlled in a coordinated fashion to cause the vehicle to follow a desired path as previously disclosed by Ilon in U.S. Pat. No. 4,598,782. Three, four, or more omni-directional wheels are connected to a suitable chassis, suspension, wheel drives, and controls to form an omni-directional vehicle. Hereinafter, all uses of the words xe2x80x9crollerxe2x80x9d and xe2x80x9crollersxe2x80x9d refer to the type of rollers used on or designed for omni-directional wheels for omni-directional vehicles.
Omni-directional wheels can be grouped into two general classifications. The first class of wheels is comprised of a rigid hub that supports a number of free spinning rollers around its periphery. The hub is rigidly coupled to an axle that, along with other omni-directional wheels and axles, supports the vehicle. The rollers are mounted at an oblique angle to the wheel""s axle and are free to rotate about their own axles. Omni-directional wheel roller mounting angles of ninety degrees have been disclosed by Blumrich in U.S. Pat. No. 3,789,947. The omni-directional wheel disclosed by Blumrich was mechanically driven to produce motion parallel to the axis of rotation of the wheel. Omni-directional wheel designs with a ninety-degree roller mounting angle and free-spinning rollers have been disclosed by Bradbury in U.S. Pat. No. 4,223,753; Hiscock in U.S. Pat. No. 4,335,899; Smith in U.S. Pat. No. 4,715,460; and Guile in U.S. Pat. Nos. D318,219 and D318,791. Omni-directional wheels with rollers mounted obliquely at roller mounting angles of approximately forty-five degrees with respect to the wheel shaft have been disclosed by Ilon in U.S. Pat. No. 3,876,255 and Amico in U.S. Pat. No. 5,701,966. U.S. Pat. Nos. 3,876,255 and 5,701,966 are hereby incorporated by reference in their entirety.
The second class of omni-directional wheels differ from the above described omni-directional wheel design concepts in that the rotational axes of the free spinning rollers intersect with the wheel""s axis of rotation. Wheels of this class have been disclosed by Bradbury in U.S. Pat. No. 4,223,753, and by Pin, et al, in U.S. Pat. No. 5,374,879. In wheels of this class, two or more spherical rollers are mounted in fixed positions so as to constrain the vehicle""s motion in the direction of wheel rotation, while being unconstrained in a direction that is orthogonal to the wheel""s axis.
In all classes of omni-directional wheels, the axle supporting each roller may be mounted to the omni-directional wheel hub at both ends of the roller, as disclosed by Blumrich, in the center, as disclosed by Ilon and Amico, or at intermediate locations, as disclosed by Smith. Typically, omni-directional wheel rollers are coated with an elastomer surface contact material to improve traction, as disclosed by Blumrich, Ilon and Smith.
The ability to move in any direction or rotate within the perimeter of the vehicle is advantageous for any industrial or commercial vehicle that must be maneuvered within confined warehouse spaces, including forklifts, scissorlifts, aircraft support and maintenance platforms, motorized dollies, and delivery trucks. Forklifts are particularly suited to omni-directional capability. As is well known in the art, forklifts are vehicles with a hydraulically or mechanically powered liftforks that are used to lift, support and position a load. Similarly, the ability to move laterally and rotate enables easy and precise positioning of onmi-directional scissorlifts and without the need for room to turn as required for a conventional scissorlift. As is well known in the art, a scissorlift is a vehicle that features a work platform suitable for supporting a worker that is hydraulically or mechanically raised or lowered to place the platform at the elevation where work is to be accomplished. Other vehicles that will benefit from omni-directional capability include wheelchairs, whether of self-propelled or unpowered designs that are well known in the relevant art. Omni-directional capability permits the wheelchair operator to maneuver freely in confined spaces such as elevators and subway cars. The ability to move laterally at will is of particular value to wheelchair operators. Omni-directional mobility is also of value for a wide variety of industrial and military uses including material transportation within a factory, aircraft maintenance, and any other use where precise, controlled omni-directional motion is desired.
Despite the known commercial need for omni-directional vehicles, none have achieved widespread commercial success due in part to the vibration and uneven ride produced by the omni-directional wheels employed to date. When a roller of an omni-directional wheel contacts the ground and assumes the load of the vehicle""s weight, the contacting surface of the roller deflects in response to the applied load. As each omni-directional wheel turns, the area contacting the ground shifts across the surface of each roller, so the portion of the roller supporting the vehicle""s weight changes as the wheel turns. As a result of the roller""s spherical, tapered or convexedly vaulted shape, the roller""s ground contacting surface compliance, which is the mathematical measure of the amount by which the contacting surface deflects in response to the applied load, varies depending upon where on the roller surface the ground is contacted. In general, elastomer-coated rollers of a smaller diameter will exhibit greater compliance than similar rollers of a larger diameter, all things being otherwise equal. For this reason, rollers are more compliant at their ends where their diameter is smaller than near their middle where their diameter is larger. In addition, rollers that are mounted to the hub by a central or intermediate attachment(s) exhibit greater compliance when the ground contacting surface spans the gap in the roller where the attachment is affixed. The varying compliance of the rollers as the wheel turns results in ride height fluctuation as the omni-directional vehicle transits a smooth surface. The ride height fluctuation causes unacceptable vehicle vibration, the magnitude of which becomes more acute at higher transit speeds.
The load capacity of a solid elastomer-coated roller is generally related to the ratio of the deflection of the elastomer when loaded to its undeflected thickness. Persons practiced in the art of designing wheels and rollers prefer a deflection-to-undeflected-thickness ratio of 0.07 to 0.15 when selecting elastomer materials and wheel diameters, and in all cases design wheels so they exhibit a ratio less than 0.25. Omni-directional wheels that use rollers with a convexedly vaulted profile, which have a smaller diameter at the ends than in the middle, are limited in load capacity to loads which are less than can be carried by a conventional wheel with the same outer diameter. Rollers that are mounted to the wheel hub by a central attachment or multiple intermediate attachments have even lower capacity due to the greater deflection that occurs when the ground contacting surface spans the gap in the roller where the attachment is affixed.
Therefore, to achieve the commercial potential of omni-directional vehicle technology, omni-directional wheel designs are needed that exhibit constant compliance while rotating under load and thus produce unchanging ride height as the vehicle transits over smooth surfaces, thereby reducing vehicle vibration. Furthermore, an omni-directional wheel with greater load capacity is needed.
This invention is an omni-directional wheel that exhibits constant vehicle ride height, low wheel vibration, and high load capacity. This invention includes a design for rollers for omni-directional wheels that produce little or no wheel rotation-induced ride height fluctuation for an expected range of loading. This invention includes the application of the low-vibration omni-directional wheels on forklift, scissor-lift and wheelchair vehicles. This invention also includes a method for designing omni-directional wheel rollers to provide low vibration performance when used on an omni-directional vehicle.
Advantages
This invention improves the ride performance of omni-directional vehicles, reducing vibration and ride height variation, thereby eliminating a major impediment to widespread commercial application of omni-directional vehicles. By reducing the amount of vibration caused by the wheel this invention enables omni-directional vehicles to operate at higher transit speeds. This invention increases the load capacity for omni-directional wheels, so that an omni-directional vehicle can be modified to carry greater loads simply by replacing the rollers with rollers designed as herein disclosed. Also, this invention reduces the peak average wheel footprint contact pressure, and thereby permits omni-directional vehicles to operate on surfaces with lower compressive strengths.